floor problem - too thin for dpm + screed

19 Aug 2004
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United Kingdom

I have a problem with my extension and the door and the floor. The floor is currently like this
As you can see the blocks are below DPC and the cavity has been filled too. The DPM comes up the inside of the block and that is my damp barrier (blue line). If I just scree to the front door then I won't have a DPM and also I'll scree over polystyrene so likely the scree will crack there. The only solution I can think of is to let in a bit of 18mm chipboard flooring. I just about have 18mm below current screed high point and I'll be using levelling compound at the end as the floor's not so flat anyway.
I'm thinking dpm under the floor board and then 3:1 motar under the DPM to bed on the blocks. Get it level then when it is dry and can screw through floor board into blocks. Through DPM of course so a bit of silicone down the screw hole to seal the hole. Floor board overlaps new screed by 50mm so is supported by new screed on inside edge.

Is there an easier way?

It would need to be something that wouldn't crack at 18mm and act as a dpm too. This bit of the floor will cold too as it is outside of the insulation so using wood will improve that. But I'm open to suggestions.


Update, might use OSB3 for flooring as I have some of that in 18mm going spare (was for flat roof, didn't need as many as I ordered in the end). I can't see any reason not to, or is there? Would moisture resistant chipboard be better as cut ends might get damp from screed.
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Your DPM should lap up over the block work and under your door.
Just screed up to the block work and then depending on your floor covering add a bit of timber to make up any difference.
The DPM should do that but it is damaged so only comes up the vertical face. The polystyrene is squishy though so I can feed a bit of DPM down to overlap it. I think I might also put a squirt of sealant down between the DPMs too to stop any wicking.

Flooring won't be tiles. Current plan is engineered wood floor but might be carpet. Walls have come down and new walls gone up. Old floor was levelled room by room so where the used to be a wall the floor heights are a little bit different hence the need to level, at least to the doorways.
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Should have said door is uPVC so DPM under door would not be needed since sill is plastic.

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